From 0d25e2d9a2a849935834e405259b4ebd8b8747d6 Mon Sep 17 00:00:00 2001
From: unintendedfraud <briceunintendedfraud@fastmail.com>
Date: Thu, 25 Apr 2024 16:37:38 +0200
Subject: [PATCH] parse statements

---
 ast/ast.go            |   8 +++
 parser/parser.go      |  95 +++++++++++++++++++++++++++++++--
 parser/parser_test.go | 120 ++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 220 insertions(+), 3 deletions(-)
 create mode 100644 parser/parser_test.go

diff --git a/ast/ast.go b/ast/ast.go
index 234a3e8..c721365 100644
--- a/ast/ast.go
+++ b/ast/ast.go
@@ -44,3 +44,11 @@ type Identifier struct {
 
 func (i *Identifier) expressionNode()      {}
 func (i *Identifier) TokenLiteral() string { return i.Token.Literal }
+
+type ReturnStatement struct {
+	Token token.Token
+	Value Expression
+}
+
+func (rs *ReturnStatement) statementNode()       {}
+func (rs *ReturnStatement) TokenLiteral() string { return rs.Token.Literal }
diff --git a/parser/parser.go b/parser/parser.go
index 2ba8ff5..9a24bef 100644
--- a/parser/parser.go
+++ b/parser/parser.go
@@ -1,20 +1,26 @@
 package parser
 
 import (
+	"fmt"
+
 	"gointerpreter/ast"
 	"gointerpreter/lexer"
 	"gointerpreter/token"
 )
 
 type Parser struct {
-	l *lexer.Lexer
+	l      *lexer.Lexer
+	errors []string
 
 	currToken token.Token
 	peekToken token.Token
 }
 
 func New(l *lexer.Lexer) *Parser {
-	p := &Parser{l: l}
+	p := &Parser{
+		l:      l,
+		errors: []string{},
+	}
 
 	p.nextToken()
 	p.nextToken()
@@ -28,5 +34,88 @@ func (p *Parser) nextToken() {
 }
 
 func (p *Parser) ParseProgram() *ast.Program {
-	return nil
+	program := &ast.Program{
+		Statements: []ast.Statement{},
+	}
+
+	for p.currToken.Type != token.EOF {
+		statement := p.parseStatement()
+		if statement != nil {
+			program.Statements = append(program.Statements, statement)
+		}
+
+		p.nextToken()
+	}
+
+	return program
+}
+
+func (p *Parser) parseStatement() ast.Statement {
+	switch p.currToken.Type {
+	case token.LET:
+		return p.parseLetStatement()
+	case token.RETURN:
+		return p.parseReturnStatement()
+	default:
+		return nil
+	}
+}
+
+func (p *Parser) parseReturnStatement() *ast.ReturnStatement {
+	stmt := &ast.ReturnStatement{Token: p.currToken}
+
+	p.nextToken()
+
+	for !p.currTokenIs(token.SEMICOLON) {
+		p.nextToken()
+	}
+
+	return stmt
+}
+
+func (p *Parser) parseLetStatement() *ast.LetStatement {
+	stmt := &ast.LetStatement{Token: p.currToken}
+
+	if !p.expectPeek(token.IDENT) {
+		return nil
+	}
+
+	stmt.Name = &ast.Identifier{Token: p.currToken, Value: p.currToken.Literal}
+
+	if !p.expectPeek(token.ASSIGN) {
+		return nil
+	}
+
+	for !p.currTokenIs(token.SEMICOLON) {
+		p.nextToken()
+	}
+
+	return stmt
+}
+
+func (p *Parser) currTokenIs(t token.TokenType) bool {
+	return p.currToken.Type == t
+}
+
+func (p *Parser) peekTokenIs(t token.TokenType) bool {
+	return p.peekToken.Type == t
+}
+
+func (p *Parser) expectPeek(t token.TokenType) bool {
+	if p.peekTokenIs(t) {
+		p.nextToken()
+		return true
+	}
+
+	p.peekError(t)
+	return false
+}
+
+func (p *Parser) Errors() []string {
+	return p.errors
+}
+
+func (p *Parser) peekError(t token.TokenType) {
+	msg := fmt.Sprintf("expected next token to be [%s], got [%s] instead", t, p.peekToken.Type)
+	p.errors = append(p.errors, msg)
 }
diff --git a/parser/parser_test.go b/parser/parser_test.go
new file mode 100644
index 0000000..ecb2420
--- /dev/null
+++ b/parser/parser_test.go
@@ -0,0 +1,120 @@
+package parser
+
+import (
+	"testing"
+
+	"gointerpreter/ast"
+	"gointerpreter/lexer"
+)
+
+func Test_LetStatement(t *testing.T) {
+	input := `
+    let x = 5;
+    let y = 10;
+    let foobar = 324453;
+    `
+
+	l := lexer.New(input)
+	p := New(l)
+
+	program := p.ParseProgram()
+	checkParserErrors(t, p)
+
+	if program == nil {
+		t.Fatalf("ParseProgram() returned nil")
+	}
+
+	if len(program.Statements) != 3 {
+		t.Fatalf("program.Statement does not contained 3 statements, got [%d]", len(program.Statements))
+	}
+
+	tests := []struct {
+		expectedIdentifier string
+	}{
+		{"x"},
+		{"y"},
+		{"foobar"},
+	}
+
+	for i, tt := range tests {
+		statement := program.Statements[i]
+
+		if !testLetStatement(t, statement, tt.expectedIdentifier) {
+			return
+		}
+	}
+}
+
+func testLetStatement(t *testing.T, s ast.Statement, name string) bool {
+	if s.TokenLiteral() != "let" {
+		t.Errorf("s.TokenLiteral() is not [let], got [%s]", s.TokenLiteral())
+		return false
+	}
+
+	letStatement, ok := s.(*ast.LetStatement)
+	if !ok {
+		t.Errorf("s is not a *ast.LetStatement, got [%T]", s)
+		return false
+	}
+
+	if letStatement.Name.Value != name {
+		t.Errorf("letStatement.Name.Value is not [%s], got [%s]", name, letStatement.Name.Value)
+		return false
+	}
+
+	if letStatement.Name.TokenLiteral() != name {
+		t.Errorf("letStatement.TokenLiteral() is not [%s], got [%s]", name, letStatement.TokenLiteral())
+		return false
+	}
+
+	return true
+}
+
+func checkParserErrors(t *testing.T, p *Parser) {
+	errors := p.Errors()
+
+	if len(errors) == 0 {
+		return
+	}
+
+	t.Errorf("parser has [%d] errors", len(errors))
+	for _, e := range errors {
+		t.Errorf("parser error: %q", e)
+	}
+
+	t.FailNow()
+}
+
+func Test_ReturnStatement(t *testing.T) {
+	input := `
+    return 5;
+    return 10;
+    return 234342;
+    `
+
+	l := lexer.New(input)
+	p := New(l)
+
+	program := p.ParseProgram()
+	checkParserErrors(t, p)
+
+	if program == nil {
+		t.Fatalf("ParseProgram() returned nil")
+	}
+
+	if len(program.Statements) != 3 {
+		t.Fatalf("program.Statement does not contained 3 statements, got [%d]", len(program.Statements))
+	}
+
+	for _, stmt := range program.Statements {
+		returnStmt, ok := stmt.(*ast.ReturnStatement)
+		if !ok {
+			t.Errorf("stmt is not *ast.ReturnStatement, got [%T]", stmt)
+			continue
+		}
+
+		if returnStmt.TokenLiteral() != "return" {
+			t.Errorf("returnStmt.TokenLiteral() is not [return], got [%q]", returnStmt.TokenLiteral())
+		}
+	}
+}